The mineralized tissues, dentin and bone, are comprised of an organic matrix in which the mineral phase becomes embedded. There appears to be a relationship between structural and compositional features of the matrix and the pattern and extent of normal deposition of the mineral phase within the matrix. Further, there appears be specific interaction between the matrix components themselves which differentiate the matrix from that of the non-mineralizing soft tissues. The objectives of this research program are to determine the nature of those features of the matrix which differentiate the hard and soft tissues, and to understand how the matrix relates to and regulates the deposition, structure and retention of the mineral phase. These broad objectives evolve into four specific problems: (1) the identification and characterization of the matrix proteins (collagen, acidic structural glycoprotein, phosphoglycoprotein); (2) interactions between the matrix components (specifically in dentin, collagen-phosphoprotein covalent bonding); (3) the physical properties of the matrix proteins and their analogs with special regard to Ca ions and phosphate ion interactions; and (4) the biosynthesis of the non-collagen matrix components and their localization at the mineralizing front. The chemistry of the phosphoprotein-collagen linkage in dentin, the chemistry of the collagen intermolecular cross-linkage in dentin and the structure of the phosphoprotein-calcium ion complex will receive special attention. A somewhat new direction will be the development of an in vitro culture system for the study of phosphoprotein biosynthesis. BIBLIOGRAPHIC REFERENCES: Semiquantitative Determination of Cyanogen Bromide Peptides of Collagen in SDS-Polyacrylamide Gels. P.G. Scott, A.G. Telser and A. Veis, Anal. Biochem. 70, 251-257 (1976). The Cyanogen Bromide Peptides of Bovine Soluble and Insoluble Collagens. I. Characterization of Peptides from Soluble Type I Collagen by Sodium Dodecylsulphate Polyacrylamide Gel Electrophoresis. P.G. Scott and A. Veis, Conn. Tiss. Res. 4, 107-116 (1976).